The present invention relates to the arrangement of a system for control and checking of the inputs and outputs of data associated with a data processing system and relates particularly to a method and an arrangement permitting an improved management of messages, sometimes termed "interrupts", emitted by the peripheral devices on the occasion of chance events occurring on the latter.
Data processing systems generally comprise a central processing system to which peripheral devices are connected. The dialogue between the central processing system and the peripheral devices is effected under the direction of a master control unit for transfer of the data inputs and outputs through what it is convenient to call channels. This master control unit for transfer of the data inputs and outputs is itself controlled by a specialized micro-logic within the machine in the form of firmware termed an Input-Output Handler (IOH), which will hereinafter be called input-output request management module. In the course of development of the logic programs, each time an input-output operation proves necessary, a logic module called a channel program is executed on a processor (specialized or unspecialized); it is this channel program which controls and checks the operation of the exchanges through the channels. The channel program once connected to the peripheral device concerned continues to execute independently of the execution of the other logic programs. The peripheral device executes to the end the orders which it will have received through the channel from the channel program.
In the course of their operation, the peripheral devices are the origin of events (interrupts) which necessitate the arbitration of the input-output request management module. These events are of two sorts. The first category, designated by EV1, is that of the TERMINATION or INTERMEDIATE events. TERMINATION events are events announcing that a channel program is terminated. INTERMEDIATE events are events announcing that a channel program has reached a well-defined intermediate stage within the channel program. The second category, designated by EV2, is that of the ATTENTION events which signal an event not linked to a channel program, for example, a change of operation occuring at the peripheral device. This is the case, for example, when an operator changes a peripheral apparatus from READY to STANDBY by pressing a push-button. The first category (EV1) comprises events known as synchronous or solicited since their existence is due to the execution of the channel program. The second category (EV2) comprises asynchronous or non-solicited events since their appearance is not the direct result of the execution of a channel program.
These events are made known to the logic by means of messages elaborated by the input-output request management module.
In a complex data processing system comprising a large number of peripheral devices, it occurred that the firmware was seized by a large number of asynchronous messages coming from one and the same peripheral device, thus masking the messages from the other peripheral devices for prohibitive time periods. The problem was therefore posed of blocking the arrival of these messages whilst avoiding losing messages.